Many power systems include an electric machine drivingly connected to a power source, such as an internal combustion engine. Such power systems often have controls that are operable to cause the electric machine to generate electricity when the power source is driving the electric machine. Using an electric machine to convert power produced by a power source into electricity enables using power from the power source to operate other electric machines. In some circumstances, it may be desirable to operate the electric machine of such a power system as an electric motor rather than an electric generator. Unfortunately, the controls of many such power systems are not capable of operating the electric machine as an electric motor.
U.S. Pat. No. 6,622,804 to Schmitz et al. (“the '804 patent”) shows a power system having an electric machine drivingly connected to an engine and controls operable to cause the electric machine to operate as an electric generator and also operable to cause the electric machine to operate as an electric motor. The power system disclosed by the '804 patent is a series type hybrid electric power system for a vehicle. The power system's controls include an electronic control unit and a power converter. The power converter is connected between the electric machine and a battery array. The electronic control unit and the power converter of the '804 patent also start the engine by operating the electric machine as an electric motor driving the engine. Subsequently, the electronic control unit and the power converter cause the electric machine to generate electricity using power from the engine.
Although the power system of the '804 patent includes controls operable to cause the electric machine to operate as an electric generator and also operable to cause the electric machine to operate as an electric motor, certain disadvantages persist. For example, employing a single power converter to regulate electric current flowing into and out of the electric machine may entail compromises. Various factors may make it desirable to transmit electricity at significantly higher rates when the electric machine is operating as an electric generator than when the electric machine is operating as an electric motor. Additionally, the power converter's power capacity for regulating the flow of electricity when the electric machine is operating as an electric motor may be the same as the power converter's power capacity for regulating the flow of electricity when the electric machine is operating as an electric generator. Accordingly, the power converter may have more power capacity than necessary for transmitting power to the electric machine when it is operating as an electric motor and/or less power capacity than desired for transmitting power from the electric machine when it is operating as an electric generator.
As a result, the overall component cost of the power system of the '804 patent may be undesirably high and/or the power system may have compromised capacity for generation of electricity. Power converters that are operable to regulate both generation of electricity by an electric machine and consumption of electricity by an electric machine operating as an electric motor are generally more expensive per unit of capacity than power converters that are only operable to regulate generation of electricity. Accordingly, configuring the power converter of the '804 patent with power capacity that is higher than necessary for operation of the electric machine as an electric motor in order to provide the desired capacity for generation of electricity may make the power converter undesirably expensive. Conversely, configuring the power converter with power capacity substantially equal to the capacity necessary for operating the electric machine as an electric motor may undesirably limit the capacity to regulate generation of electricity by the power system.
The power system of the present disclosure solves one or more of the problems set forth above.